O/T: help needed please with mini-USB connections (Garmin content)

[John Vine]

I'd appreciate some help with wiring up a mini-USB connector.

Due to my extreme carelessness, I managed to wreck the mini-USB connector on my Garmin mains charger (actually a Road Angel charger, but compatible).

I reckon this must be repairable with the help of a soldering jack plug connector.

The damaged connector looks like this:

This view from underneath shows the connections:

There are five USB pins.  The red power input connects to the top one (say pin #1).

Following a continuity test, the return (bare copper) appears to connect to two pins: #4 and #5.

Does this sound right?

JV

[Jonathan Kay]

Power ways only?

Mini-USB pinouts.

Jonathan

[John Vine]

Thanks, Jonathan -- that was quick!

I'm not sure I understand your "power ways" question, but your pin-out diagram seems to confirm that pins #4 and #5 are both ground.  I suppose if I were to cut deeper into the plug, I should be able to confirm whether the bare copper wire is indeed connected to pins #4 and #5? 

From this link (just discovered), my plug appears to be a mini-B, and requires just pin #5 to be connected to ground.

JV

[revilla]

Yes the Garmin chargers normally have a resistor between two of the pins which indicates to the unit that it is charging only. Without this the unit thinks it is connected to a computer and won't go into navigation mode. It sounds like in your case those two pins are just shorted together, kind of a zero ohms resistor, which obviously does the job. The problem with trying to make up a Garmin lead is that most USB cables don't even have a wire for the fifth pin so you can't add the resistor externally. I've got the details somewhere, let me see if I can dig them out for you.

[revilla]

John I've got a couple of documents of interest but they don't convert well to paste on here. BM me your email address and I'll mail them back to you. In a nutshell, I think the easiest way to repair it would be to buy a cheap Garmin-compatible in-car charger on eBay (for about £3 I think) which will have the necessary resistor (or short circuit) already wired into the plug, then chop the wire and splice the new tail onto your existing charger lead.

Actually, Ive just read your post again - if this is a mains charger you probably don't need it to enter navigation mode and it probably wouldn't bother you if it thought it was connected to a PC, in which case just standard USB wiring should be enough without the extra pin - I think it still charges happily in PC mode.

I dug into this when making up some leads for my Garmin to use in the car. In my case the easiest way was definitely to chop the ready made lead from a cheap Garmin-compatible cigarette socket charger and solder the larger USB plug onto the other end.

[John Vine]

Thanks, Andrew -- most interesting!

I bought this new charger, stated as suitable for Garmin Nuvi 760T satnavs (mine is a Nuvi 760).  When I plugged it in, the satnav dropped immediately into "PC-connect" mode, just as you described.  I thought that maybe the USB port was faulty, but maybe I goofed in that a 760T mains charger isn't suitable for a 760.  I've asked the seller to advise.

It certainly charged the satnav while in PC-connect mode.  But the snag is that I actually wanted to use it in navigation mode (to check through some routes I'd downloaded, and over a long period -- longer than the battery lasted). 

YHBM.

JV

[revilla]

YHBM back John.

[John Vine]

Thanks, Andrew.

Well, I've just hacked deeper into the min-USB connector, and lo and behold, pins #4 and #5 are soldered together:

So, that's one little mystery solved.

JV

 

[John Vine]

Andrew, thanks for the docs.

Inserting a section here:

Nuvi behavior depends on mini-USB plug connection. (IMHO) it is like this:
pin X not connected - data cable, nuvi connects to PC as removable drive, navigation NOT possible.
pin X & 4 short-circuited - USB supply 500mA, possible navigation,
pin X & 4 connected through 18kOhm resistor - Garmin supply 1A, possible navigation.
pin X & 4 connected through 22kOhm resistor - Garmin supply 500mA, possible navigation.

My damaged (Road Angel) charger (wiring shown above), has X and 4 shorted (no resistor), and outputs 2A.  It supports charging and navigation.

My new charger has unknown wiring and resistor (if any), and outputs 580mA.  It supports charging but not navigation.

JV
 

[John Vine]

Andrew,

You also said that "Nuvi requires 1000mA for simultaneous charging + GPS operation [many 'generic' 12VDC-to-USB adapters output a maximum 500mA]".

Certainly, Garmin recommend at least 1A output from an AC mains charger.

 

Just found this on gpsreview:

"... just plug charger in GPS and when go's into USB mode little computer at bottom of screen just unplug connector and just when the computer icon disappears Plug The Connector right Back IN and now your in charge mode . "

I tried that with my new charger.  It works!  I'm now able to use navigation mode (to review routes, etc) while the device is charging. Result!

JV